Which is sharper? Nikon, Kenko or Sigma?

[kennekam]

I am awaiting my Nikon 70-200VR 2.8 and would like to get a 2X teleconverter for it.

Which is sharper: Nikon. Keno or Sigma? I already have a Sigma, so I do not want to spend the $525 the Nikon costs in SA unless it is MUCH better than the Sigma.

I also have a Nikon 80-400VR which is a bit soft at 400mm. Is the Nikon 70-200 + 2X TC likely to be better or worse?

[dougj]

I suggest you try the Nikon SLR lens forum on dpreview.com, a very active group of Nikon users.